Center for Synthetic Microbiology (SYNMIKRO) & Faculty of Chemistry, Philipps-University Marburg, Marburg, Germany.
Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada.
Mol Microbiol. 2021 Jun;115(6):1339-1356. doi: 10.1111/mmi.14684. Epub 2021 Jan 25.
The guanosine nucleotide-based second messengers ppGpp and pppGpp (collectively: (p)ppGpp) enable adaptation of microorganisms to environmental changes and stress conditions. In contrast, the closely related adenosine nucleotides (p)ppApp are involved in type VI secretion system (T6SS)-mediated killing during bacterial competition. Long RelA-SpoT Homolog (RSH) enzymes regulate synthesis and degradation of (p)ppGpp (and potentially also (p)ppApp) through their synthetase and hydrolase domains, respectively. Small alarmone hydrolases (SAH) that consist of only a hydrolase domain are found in a variety of bacterial species, including the opportunistic human pathogen Pseudomonas aeruginosa. Here, we present the structure and mechanism of P. aeruginosa SAH showing that the enzyme promiscuously hydrolyses (p)ppGpp and (p)ppApp in a strictly manganese-dependent manner. While being dispensable for P. aeruginosa growth or swimming, swarming, and twitching motilities, its enzymatic activity is required for biofilm formation. Moreover, (p)ppApp-degradation by SAH provides protection against the T6SS (p)ppApp synthetase effector Tas1, suggesting that SAH enzymes can also serve as defense proteins during interbacterial competition.
基于鸟苷核苷酸的第二信使 ppGpp 和 pppGpp（统称：(p)ppGpp）使微生物能够适应环境变化和应激条件。相比之下，密切相关的腺苷核苷酸 (p)ppApp 参与细菌竞争期间的 VI 型分泌系统（T6SS）介导的杀伤。长 RelA-SpoT Homolog (RSH) 酶通过其合成酶和水解酶结构域分别调节 (p)ppGpp（和潜在的 (p)ppApp）的合成和降解。仅包含水解酶结构域的小分子警报素水解酶（SAH）存在于多种细菌物种中，包括机会性病原体铜绿假单胞菌。在这里，我们展示了铜绿假单胞菌 SAH 的结构和机制，表明该酶以严格依赖锰的方式随意水解 (p)ppGpp 和 (p)ppApp。虽然对铜绿假单胞菌的生长或游动、群集和抽动运动不是必需的，但它的酶活性对于生物膜形成是必需的。此外，SAH 通过 (p)ppApp 降解提供了对 T6SS (p)ppApp 合成酶效应物 Tas1 的保护，表明 SAH 酶在细菌间竞争期间也可以作为防御蛋白。
